(1) Field of the Invention
This invention relates to a process for treating tall oil fatty acids. More particularly, this invention relates to a process for treating tall oil fatty acid with a zinc catalyst and an iodine catalyst to improve the color and color stability of the tall oil fatty acids.
Tall oil is a natural mixture of rosin acids and fatty acids, together with unsaponifiable materials, which is obtained by acidifying the black liquor skimmings of the sulfate process of wood pulp manufacture, using resinous woods such as pine. The composition of tall oil varies somewhat depending upon such factors as the species of the wood which was pulped. Crude tall oil acids generally contain from about 18% to 60% fatty acids, 28% to 66% rosin acids and 3% to 24% other constituents, notably unsaponifiable materials. Crude tall oil may be distilled and fractioned to separate the fatty acid and rosin acid fractions.
Tall oil fatty acids normally consist of a major portion of mono-unsaturated oleic acids and diunsaturated linoleic acids (in approximately equal proportions), small quantities of saturated acids and unsaponifiables. Also, since tall oil fatty acids are derived from tall oil, which contains substantial quantities of rosin acids, small quantities of the latter may also be present. The Bureau of the Census of the U.S. Department of Commerce has accepted the definition of "tall oil fatty acids" as that material produced from crude tall oil which contains 90% or more free fatty acids. Most commercially available tall oil fatty acids contain substantially more than 90% fatty acids and substantially less than 10% rosin acids.
(2) The Prior Art
The color of tall oil fatty acids has hindered the desirability of their use in many applications where color is important. To attest this fact, the prior art is replicate with methods for making tall oil fatty acids lighter in color without changing the character of the fatty acids. Although the attempts to upgrade tall oil fatty acids are numerous, the following is representative of the more pertinent prior art. U.S. Pat. No. 2,515,739 to Smerechniak et al. wherein tall oil fatty acids were treated with 0.1% to 2.5% zinc to improve color. And in U.S. Pat. No. 2,763,638 to Nevin wherein tall oil fatty acids were treated with 0.05% to 2.0% zinc to improve drying properties.
Iodine is a well known catalyst for treating tall oil fatty acid. Iodine in amounts from 0.01% to 3.0% by weight has been used to disproportionate or to isomerize tall oil fatty acids as taught in such disclosures as U.S. Pat. No. 2,311,386 to Hasselstrom, U.S. Pat. No. 3,157,629 to Patrick, and U.S. Pat. No. 3,923,768 to Powers et al. Also, in U.S. Pat. No. 3,251,869 to Putnam et al., unsaturated fatty acids are treated with an iodine catalyst followed by treatment with a clay catalyst.
In contrast with the teachings of the above-described prior art, the claimed process does not use iodine in sufficient quantity for disproportionation or isomerization. The invention surprisingly obtains lighter color and better color stability using a zinc catalyst and an iodine catalyst together than is available using either alone.
It is, therefore, the general object of this invention to provide a catalyst system for treating tall oil fatty acids to upgrade their color.
Another object of this invention is to provide a process for upgrading the color and maintaining the color stability of tall oil fatty acids without changing the physical character of the fatty acids.
It is a further object of this invention to provide a process which accomplishes the above objects using in combination a zinc catalyst and an iodine catalyst.
Other objects, features and advantages of this invention will be evident from the following detailed description.